The invention relates to exhaust mufflers, and more particularly to sound-attenuating mufflers for internal combustion engines and other sources of pulsating gas flow with substantial acoustic energy transport.
The use of mufflers to reduce the exhaust noise emanating from internal combustion engines, air compressors, and the like has been a feature demanded by the need to ensure a bearable acoustic environment for persons in their vicinity. As a consequence of such need, reinforced by legal restrictions as to the amount of noise which is allowed to escape from the noise-generating device into the environment, the prior art has utilized many types of mufflers with such attenuating features as sound absorbing linings, reverse flow, cross-flow, side-branch attenuators, and Helmholtz resonators. Such mufflers are generally effective, but bulky, and require a substantial modification of the exhaust channel cross-section.
Mufflers of the prior art are generally housed in housings of elliptical cross-sections inserted in tubular pipes carrying the exhaust gas stream. The external dimensions of such cans are generally an order of magnitude larger than the flow area of the exhaust pipe proper.
The installation requirements of the sound-generating device and/or the structure in which they are housed, often render the use of such voluminous mufflers impossible. Conventionally, in motorcycles, sports-cars and special-purpose vehicles of many types, the only means for carrying the exhaust gas from the source is via a substantially tubular pipe. Attempts of the prior art to provide an effective muffler within the limitations of an elongated tubular envelope have generally failed to provide the required attenuation of sound energy, so that the terms "motorcycle" and "sportscar with straight exhaust pipe" have become synonyms for "noisy machine", for example.
The present invention provides a combination of attenuating elements in a novel structure and arrangement, thus to constitute an effective muffler for exhaust noise within a cylindrical envelope of small diameter and substantial length.
It is therefore a primary object of the present invention to teach the construction and use of a novel muffler for internal combustion engines and other sources of noisy exhaust gas flow, capable of noise-level reductions compatible with good environmental practice.
It is an object of the invention to teach the combination of sound-attenuating elements in a novel, tripartite cylindrical form; such conbinations of elements providing for a double reversal of gas flow through the muffler in a given segment.
It is an object of the invention to teach the manner in which the sound-attenuating segments of tubular muffler, each incorporating a combination of sound-attenuating elements, may be combined in a sequential structure to provide increased noise energy absorption.
It is another object of the invention to provide an effective tubular muffler of economical manufacture, adaptable to all types of stationary and mobile service, and amenable to fabrication of commonly available materials by generally understood and practiced manufacturing methods.